1. Field of the Invention
This invention relates to an alloy for the occlusion of hydrogen. This alloy can be used for the occlusion of hydrogen at a lower temperature than the temperatures required by the conventional alloys for occluding hydrogen.
Alloys for occluding hydrogen capable of directly reacting with hydrogen gas, quickly occluding the hydrogen gas in a large volume and releasing the occluded hydrogen gas have been various techniques such as the energy conversion technique applied to under development. The hydrogenation of an alloy for occluding hydrogen entails evolution of a large amount of heat of reaction. Therefore, the alloy for occluding hydrogen can be utilized for thermochemical energy conversion. Furthermore, it can be utilized for thermomechanical energy conversion by using the pressure of hydrogen occluded in the alloy and for electrochemical energy conversion by using itself as an electrode. As regards the storage of energy, this alloy can store hydrogen in a higher density than liquefied hydrogen and can store various forms of energy as converted into chemical energy. Thus, it is possible for the alloy to store energy such as heat energy, mechanical energy, and electric energy, besides storage of hydrogen gas. Specifically, practical application of the alloy for occluding hydrogen to heat pumps or secondary batteries is approaching realization.
2. Prior Art Statement
The alloy for occluding hydrogen of this nature is required to fulfill the following requirements:
(1) It should possess a hydrogen-occluding pressure and a hydrogen-releasing pressure both allowing easy treatment under working temperature conditions.
(2) It should exhibit a high hydrogen-occluding speed and a high hydrogen-releasing speed under working temperature conditions.
(3) It should allow a large amount of hydrogen gas to be repeatedly occluded and released under working temperature conditions and pressure conditions.
(4) It should be easily activated during the course of initial hydrogenation.
(5) It should produce only a small difference between the hydrogen pressure required for hydrogen occlusion and that for hydrogen release.
(6) It should possess durability high enough to permit repeated occlusion and release of hydrogen gas for a long time.
(7) It should enjoy low cost of raw materials.
As alloys for occluding hydrogen of this description, LaNi.sub.5 and FeTi have been known to the art. Unfortunately, only a few known alloys such as, for example, TiCr.sub.1.8 (Inorganic Chemistry, vol. 17, pp. 3103-3108, 1978) and Ti.sub.1.2 Cr.sub.1.2 Mn.sub.0.8 (Journal of the Less-Common Metals, vol. 89, pp. 257-262(1983) and Japanese Patent Publication SHO 59(1984)-7774) fulfill these conditions at temperatures lower than normal room temperature.
In the known alloys mentioned above, TiCr.sub.1.8 reversibly occludes and releases hydrogen gas at the lowest temperature. This alloy exhibits a hydrogen-releasing pressure of about 2 atmospheres at -78.degree. C. In order to utilize the cooling function of an alloy resulting from the release of hydrogen in a low temperature range, the alloy is required to exhibit a higher release pressure at a lower temperature than TiCr.sub.1.8.
Further, the production of TiCr.sub.1.8 possessing a stated quality requires a heat treatment to be performed at 1,000.degree. C. for three to four weeks and, therefore, entails a drawback of high cost.
It is, therefore, an object of this invention to provide an alloy which fulfills all of the requirements (1) to (7) mentioned above in a lower temperature range then TiCr.sub.1.8 and which can be produced without necessitating such a protracted heat treatment as in the production of TiCr.sub.1.8.